Many kinds of machine tools such as a grinder, for example, position the workpiece on fixed centers or V-blocks and rotate the work through a chuck on the driver spindle. In these machines, the chuck must grip the work with considerable force to assure adequate driving power. This sometimes causes problems especially if the work is fragile or easily distorted and more particularly if the chuck is designed and adapted to compensate for irregularities in or eccentricity of the work surface being chucked. The compensating mechanism used in many chucks adds so much weight that centrifugal force in use tends to bend and distort the workpiece and in any event, if the chuck is not a compensating one, the high gripping force required sometimes flexes and bends the workpiece on the fixed centers or V-block supports.